Electrostatographic liquid development apparatus

ABSTRACT

An apparatus for liquid development of an electrostatic latent image carried on an electrostatographic member. The apparatus includes at least one development electrode with roller means, the outer surface of said roller being spaced from the latent image carrying surface by a distance which ranges from greater than 30 up to about 100 microns. This apparatus produces images of low background and good image density by liquid development of electrostatic latent images.

United States Patent [191 Fukushima et al.

1 June 18, 197% 1 1 ELECTROSTATQGRAPHIC LIQUID DEVELOPMENT APPARATUS[75] Inventors: Osamu Fukushima, Tokyo;

Masamichi Sato, Asaka, both of Japan [73] Assignee: Xerox Corporation,Stamford, Conn.

[22] Filed: Jan. 10, 1972 211 App]. No.1 216,548

[52] US. Cl 118/637, 117/37 LE, l18/D1G. 23

[51] Int, Cl G03g 13/00 [58] Field of Search 118/621, 637, DIG. 23;117/175, 37 LE, 93.4 A, 93.42; 355/10 [56] References Cited UNITEDSTATES PATENTS 3,221,755 12/1965 Wright 134/122 3,345,925 10/1967Ostensen l'l8/D1G. 23

' 3,367,791 2/1968 Lein 117/37 3,405,626 10/1968 Fleisher et a1. 95/943,556,050 l/1971 Trachtenberg et a1. 1 13/637 3,601,092 8/1971 Satomi .1118/637 3669073 6/1972 Savit et al. 118/637 3.685907 8/1972 Satoetal1..... 355/17 3.687.708 8/1972 Miller 117/37 LE 3,707,139 12/1972Fukushima et al. lIH/DlG. 23 3,707,943 1/1973 Matsumoto et a1 118/7Primary Examiner-Mervin Stein Assistant ExaminerLeo Millstein [5 7]ABSTRACT An apparatus for liquid development of an electrostatic latentimage carried on an electrostatographic member. The apparatus includesat least one development electrode with roller means, the outer surfaceof said roller being spaced from the latent image carrying surface by adistance which ranges from greater than 30 up to about 100 microns. Thisapparatus produces images of low background and good image density byliquid development of electrostatic latentimages.

2 Claims, 5 Drawing Figures 1 ELECTROSTATOGRAPHIC LIQUID DEVELOPMENTAPPARATUS This invention relates to a development arrangement and moreparticularly to an apparatus for electrostatographic liquid development.

Prior electrostatographic liquid development apparatus, such as is shownin Japanese Pat. Publication No. 41-9476, have employed one or morepairs of nip rollers to convey electrostatographic sheet material.Liquid developer is'supplied on the surface of the sheet bearing anelectrostatic latent image, and conventionally the roller facing thelatent image bearing surface is constructed of a metal and operates as adevelopment electrode. The clearance between the latent image bearingsurface and the development electrode roller is maintained at arelatively small value, in a range of from 2 to microns. Because of thisnarrow clearance, small residual charges, attributable to the backgroundor highlight portions of the image, can be sensed and are developed toform an undesirably high background density. Also, when the surfacepotential of the areas of high charge density is increased by bringingthe development electrode close to the latent image bearing surface,image density is lowered because the amount of available toner in thesmall space between the two surfaces is lowered as the distancetherebetween is decreased.

It is the prime object of the present invention to avoid undesirablyhigh background density in liquid development of an electrostatic latentimage.

It is a further object of the present invention to provide a novelapparatus for liquid development of electrostatic latent image bearingsurfaces which will produce developed imageshaving reduced backgroundalong with good image density.

The present invention accomplishes the foregoing objects by theprovision of a development apparatus which overcomes the problem ofundesirably high background density by employing an increased clearancebetween the imaging surface and a roller surface of developmentelectrode means. This clearance is designed to be greater than micronsand generally up to about 100 microns whereby undesirable high-densitybackground development is prevented.

The present invention will be explained in more detail with reference tothe accompanying drawings, in which:

'to the conveying speed of the member 100. If desired,

and if streaking in the developed image can be tolerated, the roller 101may rotate at a different circumferential velocitythan the rate ofadvancement of member 100, or even in a reverse direction relative tothe advance of the member 100.

The electrostatographic member can have any suitable configurationincluding drums, webs, belts or plates. Although the embodiments ofFIGS. 1-4 cannot use drums, the development electrode configuration ofthe present invention can readily be adapted thereto. Any surface whichis capable of receiving and holding a charge pattern for a short periodof time can be suitably employed. Typical photoconductive materials in-FIG. I is a side view of a basic embodiment of the include selenium,selenium alloys and binder compositions comprising zinc oxide, cadmiumsulfide, cadmium sulfo selenide, and the organic photoconductorsincluding phthalocyanine binder coatings and polyvinyl carbazole.Particularly preferred photoconductive materials are selenium orselenium alloy coated members having a conductive base, paper coatedwith a zinc oxide binder layer and paper coated with a phthalocyaninebinder composition. More particularly preferred for use in the presentinvention are electrostatographic surfaces comprising organic orinorganic photoconductive binder compositions applied to suitable webssuch as, for example, paper coated with a zinc oxide binder layer or aphthalocyanine binder layer. Such electrostatographic surfaces can beemployed conveniently and economically on a one-time basis therebyeliminating the need for cleaning the surface prior to re-use. Latentelectrostatic images are conventionally formed on such photoconductiveelectrostatographic surfaces by uniformly charging them'in the dark, forexample by a corotron, and then exposing them to a light and shadowimage to selectively discharge the surface, as taught, for example, inU.S. Pat. No. 2,297,691 to C. F. CarlsonThe electrostatographic surfaceneed not be photoconductive. It can be any suitable surface capable ofretaining a latent image applied, for example, by direct application ofa charge in image configuration or by transfer of an electrostaticlatent image from another member. Suitable materials may include varioushigh polymeric materials such as polyethylene terepthalate andpolytetrafluoroethylene.

A roller 102 is positioned just beneath the roller 101 and rotates atthe same speed as the conveying speed of the electrostatographic member100. The roller 102 is arranged in a contact engagement with the rearsurface of the electrostatographic member. The roller 101 is necessarilymade conductive so as to effectively ab- .case a sheet, is conveyed inthe direction shown by the arrows, having a latent imagebearing surfacefacing upward. A development electrode means comprising roller 101 ispositioned such that the surface of the roller has a clearance rangingon the order of from greater sorb the electrostatic lines of forceemanating from the charges of the latent image on the member 100. Forsuch purpose the roller 101 may be constructed of plastic having asurface coating of a metal, or of metal which is surface-treated to havea thin insulating layer. Rollers 103 and 105 are arranged along oppositesides of the roller 101 with the rotational axis of the respectiverollers paralleling each other along the movement path of the member100. The rollers are each intended to rotate at the same circumferentialvelocity as the advaricing speed of the member to thereby convey andposition said member.

Mating rollers 104 and 106, which form roller pairs together withrollers 103 and 105, respectively, further aid in regulating the speedand position of member 100.

These pairs of regulating rollers nip and convey the member 100. Therollers 103 and 105 are electrically insulative or semi-conductive andhave a smooth, rigid surface. Practical examples of materials for theconstruction of the rollers 105 and 103 include glass, various hardplastics, ceramics, etc. No essential limitation is imposed onto thestructure or electric properties of the lower surface rollers 102, 104and 106, suitable materials including metal, rubber, plastic, etc. Anoule 107 is provided above the electrode roller 101, to spray developerliquid onto the surfaces of the roller 101 from above. The developerliquid is fed to and circulated by a pump, not shown in the figure, andsupplied to the nozzle 107.

The developer liquid can comprise a suspension of finely dividedparticles in a dielectric liquid. The liquid itself must be sufficientlyinsulating to prevent dissipation of the electrostatic charge pattern onmember 100. This generally requires a volume resistivity in the order 10to l ohm-centimeters or greater. Suitable liquids include among othersnormal heptane, normal hexane, petroleum ether and various commercialpetroleum solvents having volatility in the kerosene to gasoline range.Suitable liquids of this latter type include Sohio Odorless Solvent No.3440, available from the Standard Oil Company of Ohio; commercialkerosene; Shell 140 solvent and Shell 8230 insecticide base, bothavailable from the Shell Chemical Corporation; and Soltrol 130,available from the Phillips Petroleum Company. Where non-flammableliquids are desired, use can be made of carbon tetrachloride,tetrachloroethylene, trichloro-ethylene, and trichloro-trifluoroethane.Various other liquids having the necessary resistivity can also be usedas the liquid component of the developer liquid. The particles used inthe developer liquid may also comprise various types. They may, forexample, comprise finely divided pigmented resin particles of the vinyl,acrylic or other types, finely divided dry pigments, fine particles ofdyes insoluble in the dielectric liquid employed, or artists oilpigments disperse in the liquid.

As the member 100 is held by the two pairs of rollers, 103/104 and105/106 and its position thereby regulated, the roller 101 as is shownwill not come in contact with the surface of the member 100, and thedistance between the roller 101 and the latent image bearing surface ofthe member 100 remains at the clearance distance range of greater than30 up to about 100 microns.

FIG. 2 illustrates another preferable embodiment of the invention, inwhich electrode rollers 201, 202, 203 and 204, are provided along withregulating rollers 211, 212, 213, 214 and 215. Mating rollers 221, 222,223, 224, 225, 226, 227, 228 and 229 are provided, facing or contacting,through the member 100, any one of the electrode or regulating rollers.In the apparatus shown in FIG. 2, multiples of the unit arrangementsshown in FIG. 1 are employed along the arcuate path of the member 100.As the member 100 advances along the arcuate path, the rear surface ofthe member 100 is pushed toward the rollers 221 to 229, thereby morestrictly regulating and stabilizing the position of the latent imagecarrying surface, leaving the above stated requisite clearance range offrom greater than 30 up to about 100 microns between the latent imagecarrying surface of member 100 and the surfaces of the electroderollers.

In FIG. 3, illustrating a further embodiment, electrode rollers 301,302, 303 and 30 1 and regulating rollers 311, 312, 313, 311 and 315" areprovided around a relatively large diameter cylinder 320 facing towardthe electrode and regulating rollers. The cylinder 320 corresponds tothe rollers 102, 10 1 and in FIG. 1 and 221 to 229 in FIG. 2, and may beconstructed from similar materials. The member 100 is conveyed aroundthe cylinder 320, with the imaging surface away from the cylinder, underthe application of suitable tension, and the predetermined clearancerange as stated above can be maintained relative to the electroderollers.

In FIG. 41, illustrating still another embodiment, electrode rollers41-01, 102, 403 and 10 1, and regulating rollers 4111, 412, 4113, 11 1and 15 are provided on the upper plane of an endless belt 120 which issuspended between and driven around two rollers 121 and 422. The endlessbelt 420 is positioned so as to allow the predetermined clearance rangeas stated above relative to the electrode rollers 101 to 10 1. The belt4120 is driven at a constant speed in contact engagement with theregulating rollers 111 to 115. The belt 420 may be made of cloth,rubber, plastic, metal, or metal mesh. When an electrostatographicmember 100 is placed on the upper plane of the endless belt 420, it isnipped between the belt and the rollers 111, 412, 4113, 11 1 and wherebythe member 100 is conveyed, for example, in the direction shown by thearrow, and developed.

As noted briefly above, it has been discovered that liquid developmentsystems prior to that of the present invention suffered from severaldisadvantages because it was thought to be necessary to maintain thedevelopment electrode surface closely spaced from the latent imagecarrying surface. Spacings of from about 2-20 microns had been used,with the lower end of this range being desirable. It is the unexpecteddiscovery of the present invention that by increasing this spacing towithin the range of from greater than 30 to about 100 microns, it ispossible to achieve a dramatic decrease in background density whileachieving good image density. While not wanting to be bound to anytheories, it presently appears that this effect is a result of twophenomena. Firstly, the effect of the development elec trode is sointense at small clearances that any residual charge remaining inexposed areas can cause develop ment to a considerable extent. Thiscauses undesirable, high-density background development. Secondly, itfurther appears that when the development electrode is brought close tothe latent image bearing surface, the amount of developer liquidmaintained in the small clearance may be inadequate to give a developedimage of good density.

FIG. 5 presents a comparison of developed images prepared according tothe present invention, and those prepared according to the priorsystems. A representative clearance, between the electrode surface andthe latent image bearing surface, of 5 microns is used for the prior artsystem, and a representative clearance of 50 microns is used for thepresent invention. In each case, the latent image is developed and thedensity of the copied image is plotted against the density of theoriginal image. A 45 line, Le, a line with a slope of 1, is close toideal. That is, when the line has a slope of 1, the original anddeveloped image densities will be the same. As noted from FIG. 5, thepresent invention closely approximates ideal reproduction over a rangeof values which far exceeds that of the prior art system. The curve forthe prior art system is quite flat and shows poor uniformity, while thecurve of the present invention contacts or closely parallels the idealfor a substantial distance. Thus, the present invention allows greaterdesign flexibilityand permits the uniform production of high qualitycopies of good density and low background.

Other possibilities and arrangements employing the inventive concept maybe employed. For example, in each of the embodiments shown hereinbefore,the role of the upper and lower rollers may be reversed or the relativeposition of roller and belt may be reversed. Further, in the fundamentalarrangement of rollers shown in FIG. 1, one electrode roller was set upbetween the regulating rollers 103 and 105, however, multiple electroderollers may be provided. The same situation holds true for the otherembodiments. Also, the roller facing toward an electrode roller (102 inFIG. 1, for example) may be omitted. Further, the device can employ arigid, drum-shaped photoconductor, in which embodiment the regulatingrollers can be dispensed with.

While the invention has been described with reference to specificembodiments, it will be understood by those skilled in the art thatvarious further modifications and alternative structures andcombinations thereof may be made and equivalents substituted withoutdeparting from the true spirit and scope of the invention.

What is claimed is:

1. An electrostatographic liquid development apparatus comprising afirst and second pair and at least one additional pair of regulatingrollers, to convey an electrostatographic member carrying anelectrostatic latent image on a surface along a predetermined path, eachpair of regulating rollers respectively positioned on opposite sides ofsaid electrostatographic member along said predetermined path androtating therealong to nip and convey said electrostatographic memberalong said.

electrostatographic member carrying an electrostatic latent image on asurface thereof remote from said continuous surface, a plurality ofregulating means cooperating with said continuous surface for nippingand conveying said electrostatographic member, said plurality ofregulating means including a first and second pair and at least oneadditional pair of regulating rollers contacting saidelectrostatographic member at locations along said predetermined path,electrode means including a roller surface positioned between saidregulating means, the roller surface of said electrode means positionedabove said latent image carrying surface with a constant clearanceranging from greater than 30 up to about 100 microns relative to saidlatent image carrying surface, each of said pairs of regulating rollersseparated from the next successive pair of regulating rollers by saidelectrode means, and developer emitting nozzles positioned above saidelectrode rollers.

1. An electrostatographic liquid development apparatus comprising afirst and second pair and at least one additional pair of regulatingrollers, to convey an electrostatographic member carrying anelectrostatic latent image on a surface along a predetermined path, eachpair of regulating rollers respectively positioned on opposite sides ofsaid electrostatographic member along said predetermined path androtating therealong to nip and convey said electrostatographic memberalong said path, electrode means including a roller defining saidelectrode surface positioned between each of said pairs of regulatingrollers so that each pair of said regulating rollers is separated fromthe next successive pair of regulating rollers by said electrode means,said roller surface of said electrode means positioned along said pathwith a clearance ranging from greater than 30 up to about 100 micronsrelative to said latent image carrying surface of saidelectrostatographic member.
 2. An electrostatographic liquid developmentapparatus comprising a continuous surface for conveying anelectrostatographic member carrying an electrostatic latent image on asurface thereof remote from said continuous surface, a plurality ofregulating means cooperating with said continuous surface for nippingand conveying said electrostatographic member, said plurality ofregulating means including a first and second pair and at least oneadditional pair of regulating rollers contacting saidelectrostatographic member at locations along said predetermined path,electrode means including a roller surface positioned between saidregulating means, the roller surface of said electrode means positionedabove said latent image carrying surface with a constant clearanceranging from greater than 30 up to about 100 microns relative to saidlatent image carrying surface, each of said pairs of regulating rollersseparated from the next successive pair of regulating rollers by saidelectrode means, and developer emitting nozzles positioned above saidelectrode rollers.